The use of tools to form and machine ferrous metals, such as stainless steel, is well known in various industries. One industry, for example, to which the present invention applies, is the manufacture of head suspensions for rigid disk drives from stainless steel sheet material as are used within the data storage industry. In such an application, tooling is typically used to cut, shape, and form the various components of a head suspension, including a base plate, a load beam, longitudinal rails along the load beam, a flexure, and a dimple in either the load beam or the flexure used as a load point during operation of the head suspension. To form stiffening rails along the side of a load beam, a rail punch having a rounded surface is used to form the longitudinal rails of the load beam by engaging and plastically deforming the edges of the material of the load beam. Similarly, a dimple forming punch can be used to engage a flat region of the load beam or the flexure to deform a "load point" dimple from the material thereof. Traditionally, tools such as a rail punch, a dimple punch and dimple socket incorporate tool steel or tungsten carbide cermet on wear surfaces to engage and form the ferrous stainless steel.
The use of tools to engage and frictionally guide ferrous metals such as stainless steel is also well known in various industries, including the manufacture of head suspensions. In such an application, a guide tool engages and moves a piece of ferrous metal over a surface. Friction between the ferrous metal and the guide surface over which it is moved generates heat and abrades the surface of the ferrous metal and/or the surface of the guide tool. For example, a pin in a base plate guide can be used to engage and guide a suspension base plate over an inclined surface and into alignment with a suspension load beam for attachment of the base plate to the load beam. As with tools used in forming operations of ferrous metal, the wear surfaces of guide tools over which ferrous material are frictionally moved traditionally incorporate tool steel or tungsten carbide into the guide surface.
The use of tools having a polycrystalline diamond (PCD) surface to machine or form non-ferrous materials is also well known in various industries. For example, PCD tooling is currently used in the machining and forming of aluminum, copper, brass, plastics, granite, fiber plastics such as Kevlar, wood and wood-based products, ceramics, and carbide. PCD is known for superior performance characteristics, and tools with a PCD surface often have a useful life that is 50 to 200 times greater than tools having tool steel or tungsten carbide cermet surfaces. Tools having PCD surfaces are thus desirable for repetitive operations such as cutting, turning, forming and milling. In addition, PCD exhibits a lower coefficient of friction against most materials than does tool steel or tungsten carbide cermets, and transfer of workpiece material to PCD is limited because of the inherently low surface energy of PCD. Build-up of workpiece material on a tool surface over usage increases the surface roughness. PCD tools generally maintain a smoother surface than conventional tools during metal forming, thus creating a smoother finished surface on the workpiece. A smooth PCD surface also leads to lower friction against the workpiece material, thus reducing or eliminating the need for lubricants in the machinery or forming process.
It is also well known and conventionally accepted, however, that PCD tooling can only be efficiently used on non-ferrous materials. A primary disadvantage of PCD, and PCD tooling, is that diamond is generally incompatible with ferrous metals because carbon, the base element of diamond, is soluble in iron. In other words, PCD tooling cannot effectively be used to frictionally guide, machine, or form ferrous materials because diamond dissolves and diffuses into the material due to the iron content of the material. Additionally, at temperatures above about 700 degrees Celsius, iron catalyzes the transformation of PCD surfaces to graphite, also known as "graphitization," which subsequently creates problems. First, graphite is a soft form of carbon and wears very poorly. This leads to reduced tool life and introduces graphite particles into the machining or forming process as the tool surface wears. In addition, carbon readily diffuses into iron at a rate that increases with temperature. As such, the PCD surface soon becomes too rough for proper use, or the tool wears rapidly and is unable to meet specifications for geometry and performance after a very short period. Because the local surface temperatures of metal during forming and machining operations can easily exceed 700 degrees Celsius, PCD tools are not used to frictionally guide, form, or machine iron-based materials.
Attempts have been made to artificially cool ferrous materials below 700 degrees Celsius during machining operations, thus allowing them to be machined using PCD tools. Researchers have attempted to use liquid nitrogen as a cooling agent when machining ferrous materials with PCD tools, thus reducing the high temperatures that cause graphitization and the PCD tool to dissolve and diffuse. However, the high cost of delivering and using liquid nitrogen as a cooling agent makes such a process economically unfeasible. The use of cooling agents also reduces the PCD tool's resistance to fracture, commonly known as the "fracture toughness." This is because cobalt is used as a binder for the PCD tooling, and at or near liquid nitrogen temperatures, the cobalt binder becomes increasingly brittle. As such, the fracture toughness of the PCD tool can be lowered by as much as 70%. In addition, the use of a cooling agent, or a lubricant of any sort, during machining or forming operations may introduce particles and/or other contaminants into the process, which is not desirable for precise operations. For these reasons, PCD tooling cannot generally be used to machine or form ferrous materials in an efficient manner, and cannot be effectively used in precise operations where contamination by a cooling agent is a concern.